Manufacture of semiconductor integrated circuits and other micro-scale devices typically requires formation of multiple metal layers on a wafer or other substrate. By electroplating metals layers in combination with other steps, patterned metal layers forming the micro-scale devices are created.
Electroplating is performed in an electroplating processor with the device side of the wafer in a bath of liquid electrolyte in a vessel, and with electrical contacts on a contact ring touching a conductive seed layer on the wafer surface. Electrical current is passed through the electrolyte and the conductive layer. Metal ions in the electrolyte plate out onto the wafer, creating a metal layer on the wafer.
Electroplating processors typically have consumable anodes, which are beneficial for bath stability and cost of ownership. For example, it is common to use copper consumable anodes when plating copper. The copper ions moving out of the plating bath to form the plated copper layer on the wafer are replenished by copper ions coming off of the anodes, thus maintaining the copper ion concentration in the plating bath. This is a cost effective way to maintain the concentration of metal ions in the bath compared to replacing the electrolyte bath. However, using consumable anodes requires a relatively complex and costly design to allow the consumable anodes to be periodically replaced. If the anodes are replaced through the top of the chamber, then the electric-field shaping hardware is disturbed requiring re-checking the performance of the chamber. If the anodes are replaced from the bottom of the chamber, then extra complication is added to the chamber body to easily remove the lower section of the chamber and add reliable seals.
Even more complexity is added when consumable anodes are combined with a membrane (for example a cation membrane) to avoid degrading the electrolyte, or oxidizing the consumable anodes during idle state operation, and for other reasons. Cationic membranes allow some metal ions to pass, which lowers the efficiency of the replenishment system and may require an extra compartment and electrolyte to offset loss of metal ions through the cationic membrane.
Electroplating processors using inert anodes have been proposed as an alternative to using a consumable anode. An inert anode processor may reduce complexity, cost, and maintenance. However, use of inert anodes has led to other disadvantages, especially related to maintaining the metal ion concentration in a cost effective manner compared to consumable anodes, and the generation of gas at the inert anode which can cause defects on the wafer. Accordingly, engineering challenges remain to providing an inert anode electroplating processor.